In general, a target object is inspected whether the target object is properly formed before and after the target object is formed on a substrate, in order to enhance a reliability of the substrate having the target object formed thereon. For example, a solder paste formed on a substrate is inspected before an electronic device is mounted on the substrate through the solder paste, or an electronic device is inspected whether the electronic device is properly mounted on a substrate after the electronic device is mounted on the substrate through a solder paste.
Recently, a three dimensional inspecting method using a substrate-inspecting apparatus having at least one projection module and an inspecting module, is used for a precise inspection. The projection module includes a light source and a grid pattern for projecting patterned light, and the inspecting module includes a camera for capturing an image formed by the patterned light when the patterned light is reflected by a target object.
The substrate-inspecting apparatus may inspect all regions of the substrate at once. However, when the size of a substrate is greater than a field of view FOV of the camera, the substrate-inspecting apparatus may inspect a plurality of divided regions of the substrate step by step.
When the substrate is inspected by the substrate-inspecting apparatus, both end portion of the substrate is fixed and supported. Therefore, in case of a large sized substrate, the substrate may have warpage, so that there exists a height deviation among the plurality of divided regions. In general, the substrate-inspecting apparatus has a tolerance for a height deviation. Therefore, when the height deviation induced by the warpage of the substrate exceeds the tolerance, the height of a target object cannot be inspected properly.
When the substrate has a warpage to induce height deviation among inspection regions, the height deviation among the inspection region is firstly measured by a laser range finder and the height of the inspecting module is adjusted by using the height deviation. However, the above method increases inspection time.